Sheet feeding apparatus

ABSTRACT

Apparatus for feeding sheets includes a feed table onto which the sheets are supplied. The front edges of the sheet are engaged by stops, and suction openings in the feed table precede the stops. Suction conduit means which underlie the feed table in alignment with the suction opeings are operable between raised and lowered positions in sychronism with the operation of the apparatus whereby the underpressure applied to a sheet through the suction openings and suction conduit to hold down the sheet on the feed table is varied in synchronism with the operation of the apparatus as the feed conduit means is raised and lowered.

'llnlte States Patent 1191 .lesclrke et al.

[ SHEET FEEDING APPARATUS [75] Inventors: Willi Jeschke; Gerhard Pollich, both of Heidelberg, Germany [73] Assignee: Heidelberger Druckmaschinen Aktiengesellschaft, Heidelberg, Germany 22 Filed: July 12, 1972 21 App1.No.:271,066

[30] Foreign Application Priority Data July 13, 1971 Germany 2134834 52 us. (:1... "211/231, 27 19s 511 1m. (:1 ..'.j. B6571 9/04, B65h 9/14 58 Field of Search... 271/60, 46, 74 R, 50, 74 MS,

[56] References Cited UNITED STATES PATENTS 2,753,184 Backhouse 271/46 X 1451 Aug. 13, 1974 3,140,030 7/1964 Stewart 271/74 X Primary Examiner-Evon C. Blunk Assistant Examiner-James W. Miller Attorney, Agent, or FirmHerbert L. Lerner 5 7] ABSTRACT Apparatus for feeding sheets includes a feed table onto which the sheets are supplied. The front edges of the sheet are engaged by stops, and suction openings in the feed table precede the stops. Suction conduit means which underlie the feed table in alignment with the suction opeings are operable between raised and lowered positions in sychronism with the operation of the apparatus whereby the underpressure applied to a sheet through the suction openings and suction conduit to hold down the sheet on the feed table is varied in synchronism with the operation of the apparatus as the feed conduit means is raised and lowered.

7 Claims, 6 Drawing Figures PATENTEU AUG] 31314 sum 2 or z SHEET FEEDING APPARATUS This invention relates to a sheet-feeding apparatus and more particularly to a sheet-feeding apparatus in which successive sheets which may partially overlap or which have no overlap are supplied to a feed table. Stops are provided at the forward edge of the feed table and a plurality of suction openings disposed in the feed table hold down the leading edge of the sheet. The arrangement is such that the incoming sheet is reliably guided under catch hooks on the front stops even at relatively high rates of feeding of the sheets, thereby assuring dependable and trouble-free alignment of the feed-in sheet.

Sheet feeding devices are known in which suction means are arranged in the plane of the top of a feed table to hold down the sheet on the feed table. These known suction means include stationary turbulence or whirling chambers which are open at the top. In order to obtain a reduced pressure to hold the sheet down on the feed table, compressed air is fed in through an inlet which directs an air stream tangentially into the turbulence chamber. J

The manufacture of such turbulence chambers is relatively expensive. Also the suction openings of the turbulence chambers are so large that the sheets being fed on the feed table can catch in such openings either because of bent corners on the sheet or because of excessive suction in localized areas. However, the most important drawback of the above known sheet feeding device is its great sensitivity to difference in paper thickness such that the reduced pressure in the suction means produced by the compressed air cannot be regulated finely enough. Furthermore, the air tends to flow over the edges of the turbulence chambers, thereby preventing the sheet from lying flat against the top of the feed table which is necessary for exact alignment.

In another known sheet-feeding device, the top of the feed table is provided with slots through which compressed air is blown in a direction toward the feed stops. The slots are arranged such that the compressed air passing through the slots produces an underpressure which holds down the leading edge of the incoming sheet. A disadvantage of this known arrangement is that in guiding the sheet under the hook-shaped front stops, unless the compressed air is carefully controlled, the leading edge of the sheet will flutter. Precise and exact control of the compressed air for producing the required under pressure, however, presents difficulties at printing speeds which'must be adjustable, for example, from 4,000 to 10,000 prints per hour. Accordingly, instability of the sheet cannot be avoided. However, in order to obtain precise alignment, an absolutely flat condition of the sheet, which is pushed against the front stops, is required on the feed table. 1

In other known sheet-feeding apparatus slots are provided in the feed table plate immediately ahead of the front stops. A concave guide member is disposed underneath the slots and compressed air is blown against the guide member. Byadjusting the guide member in relation to the arriving stream of air it is possible to vary the amount'of underpressure produced above the slots. However, the concave guide member and the associated parts of this known sheet-feeding apparatus must be accommodated in the area where customarily the control devices for the front stops and pull guides are located. It is therefore extremely difiicult to mount this known apparatus for producing underpressure at the intended location underneath the feed table plate. In addition, the same difficulties can be expected with this known arrangement as heretofore described in connection with other known apparatus as related to the generation of underpressure by compressed air.

Also known are sheet-feeding apparatus in which suction chambers, over which perforated conveyer belts run, are arranged in the feed table immediately ahead of the frontstops. The use of such conveyer belts has the disadvantage, in that after extended use, wear of the belt material occurs and results in disruptions and malfunctioning in the feeding of the sheets. Such disruptions and malfunctioning are of the type in which the printer cannot definitely and immediately ascertain the source. Moreover, a mechanic is needed to change such worn-out conveyer belts. Not insignificant is also the high air losses which occur when perforated conveyer belts are used.

Finally, there is known a sheet-gripper and straightening arrangement which consists of rotating suction discs. These suction discs are located in the feed table and have a number of suction openings, which function to move the incoming sheet against the lateral and front stops and to pass the sheet on after it is straightened. This arrangement is very expensive and offers no adequate assurance of an exact alignment of the fed-in sheets in modern high-speed printing machines.

An object of the present invention is to provide a relatively simple device which is operable to pull an incoming sheet immediately ahead of the front stops absolutely flat against the feed table platform and to place it without affecting the mobility of the sheet during the alignment process.

According to the present invention, the aforementioned object is achieved by providing a plurality of suction openings arranged such that in the area of each group of suction openings a suction pipe opens at the bottom side of a feed table plate. The end of each suction'pipe essentially covers up the associated group of suction openings, and the distance between the end of the suction pipes and the underside of the feed table plate is variable in accordance with the rate of feed of the sheets.

Due to the arrangement of several suction pipes with relatively large cross-sectional suction areas, a large volume of air is drawn in per unit of time, but only a slight underpressure is obtained. As a result the incoming sheet lies flat against the feed table plate even though the leading edge of the sheet may be initially somewhat raised. Consequently, a reliable construction is provided in which the sheets enter under the hooks of the front stops. in this regard the gap between the hooks and the feed table plate is only a few millimeters. The hooks at the front stops are necessary so that the leading edge of the sheet cannot escape upwardly during the alignment of the sheet in which case an unfavorable effect on the registration would result. According to the present invention the ability of the sheet to slide over the feed table plate is not impaired and excessive local sticking of portions of the sheet at the feed table plate cannot occur because of the very small underpressure.

The ability of the pulled-down sheet to easily slide on the feed table at high feeding speed is assured only if,

to the extent possible, no underpressure or only slight underpressure exists at the moment when the sheet is aligned. Accordingly at high sheet feeding speeds, a correspondingly fast change of the underpressure is desirable. To this end even a slight lowering of the suction pipe by a few millimeters relative to feed table reduces considerably the underpressure prevailing above the feed table plate, because the suction pipes then mainly draw in air on the underside of the feed table plate rather than through the suction openings on top of the feed table plate.

An advantage in one embodiment of the present invention resides in the fact that the suction pipes lead into a main vacuum line in which a regulating valve is provided. The regulating valve can serve, on one hand, to provide an adjustment for obtaining the optimal underpressure, and on the other hand, to re-adjust the suction action when changing the type of sheets being handled, for example, when changing from cardboard to paper or to onion-skin. Connecting the suction pipes to a main vacuum line makes it possible, in a very simple manner, to add or disconnect individual suction pipes depending on the width of the sheets being fed at any particular time.

An embodiment of the invention willnow be described in greater detail with reference to the accompanying drawings, wherein:

FIG; 1 is a side elevational view of a sheet-feeding apparatus according to one embodiment of the invention showing the front stops lifted and the suction pipes in a raised position and with all known elements of the sheet feeder omitted;

FIG. 2 is a plan view of the control parts shown in FIG. 1;

FIG. 3 is a side elevational view of the embodiment in FIG. 1, but showing the first stops in a lowered position for aligning the sheet and with the suction pipes in a lowered position;

FIG. 4 is a schematic plan view of a portion'of the suction apparatus;

FIG. 5 is an elevational view partly in section of a portion of the suction apparatus; and

FIG. 6 is a top view of a portion of the suction apparatus.

Referring to the drawings, FIG. 1 shows sheets 2 which are supplied one by one to afeed table plate 1 of a sheet-feeding apparatus. At the lower end of the feed table plate 1 are located several front stops 3 having catch hooks 4 and which intercept the incoming sheet 2. The front stops 3 are operated and the sheets are aligned by means of front stop member 5.

The front stops 3 are mounted on a shaft 6 rotatably in such a manner that an auxiliary gripper 29 provided above the feed table plate 1 is operable to grip the aligned sheet 2 and pass it on to agripper set 7 on a printing cylinder 8. The sheet gripped by the gripper set 7 will hereinafter be referred to as the departing sheet The shaft 6 is mounted on one end of a' pivotal lever 10 which is pivotalv about the shaft 25. At the same end of the pivotal lever 10, a suction pipe 11 is attached by,

means of a clamp 12. The suction pipe 11 leads downwardly into a flexible connecting tube 13.,The free end 14 of the suction pipe 11 terminates at the underside of the feed table plate 1.

drawings show the suction openings 15 as circular holes. However, these suction-openings 15 may have other configurations, for example, they may be elongated holes.

As may be seen in FIG. 4, the suction openings 15 are arranged and combined to form four groups 16 to 19. Each of the groups 16, 17, 18, 19 is disposed immediately in front of one of the front stops 3. One end 14 of each of a plurality of suction pipes 11 is located underneath each group 16 to 19 of the respective suction opening 15.

Each of the flexible connecting tubes 13 leading from the suction pipes 11 leads to a regulating valve 20 which is connected to an exhaust blower 22 via a flexible main vacuum tube 21. The regulating valve 20 serves as an adjustment to obtain the optimum operating underpressure. For the handling of onion-skin paper, paper and cardboard, for instance, a different underpressure must be obtained.

As shown in FIG. 5 each group 16, 17, 18, 19 of suction openings 15 can be accommodated, in a separate suction disc 23 which is inserted into a recess 24 in the feed table plate 1. The suction discs 23 are made of a material having a low friction coefficient, for example, Teflon or Fluon. As a result the suction disc 23, which is flush with the upper surface and with the lower surface or underside of the feed table plate 1 presents a particularly low frictional resistance to the pulled-down sheet, whereby smearing of the printed underside of the sheet is avoided in cases where the ink is not sufficiently dry.

The suction pipe 11, in its suction position, has its end 14 located immediately underneath the suction disc 23. Depending on the vertical position of the pipe end 14 relative to the suction disc 23, more or less bypass air is drawn in from the underside of the feed table plate 1 and the underpressure prevailing above the suction openings 15 for holding down the sheet also changes accordingly. The pipe end 14 in cooperation with the underside of the feed table plate 1, thereby serves as a highly effective control valve inasmuch as it is located immediately at the area where the suction is applied. In the open condition, this control valve, furthermore, has no additional flow resistance of any kind. The cross-sectional area of each suction pipe 11 is made relatively large so that a large amount of air is drawn in but only a relatively small underpressure is produced. The extremely rapid action of the above described control valve also makes possible a substantial reduction of the already low underpressure in the operating cycle of the machine even at the highest feeding speeds that may occur.

As previously described, the suction pipe 11 is attached to the lever 10. The latter in turn is pivoted on the shaft 25 and is rocked through a predetermined angle by a cam 26 through a cam follower 27 in accordance with the operating cycle of the machine. As the lever 10 is rocked, the catch hook 4 of the front stop 3 is lowered and raised. The end 14 of the suction pipe 11 is also lowered and raised; the amount of travel between lowered and raised positions being indicated by the numeral 28 in FIG. 5. In the lower position of the suction pipe 11, the underpressure which is applied to the sheet above the feed table plate 1 is naturally lowest, if not zero. At this position of the suction pipe 11, thesheet is aligned by the front stops 3 and the pull guides and any other influence on the sheet during this part of the operating is undesirable.

In order to adapt to different sheet sizes, the two outer of the four suction pipes 11 provided, as shown in FIG, 4, may be disconnected. However, as may be desirable, the inner suction pipes 11 may be disconnectedor regulated separately, particularly in cases where it is desirable to exert increased suction action on the corners of the sheet which, in many cases tend to deflect upwardly. For this reason, valves 30 are provided in the individual flexible connecting tubes 13 to control and regulate the suction applied through each suction pipe 11. r

A discription of the operation of the apparatus follows. Sheets 2 are supplied one by one in rapid succession over the feed table plate 1 to the front stops 3. In order to prevent the leading edges of the sheets 2 from turning up, in spite of the high feeding speed, and thereby pass over the catch hooks 4 of the front stops '3, .the exhaust blower 22 draws off a considerable amount of air via the suction pipes 11 and the suction openings above the feed table plate 1. As a result a slight underpressure is produced above the feed table plate 1 which pulls the leading edge of the incoming sheet 2 absolutely flat against the upper side of the feed table plate 1. Thus, it can be relied upon that the incoming sheets 2 will arrive under the catch hooks 4 of the front stops 3.

In this phase of the feeding of the sheet, the suction pipes 11 are in the position indicated in FIG. 1 in which the pipe ends 14 are disposed immediately under the feed table plate 1 so that air is drawn through the suction openings 15. However, as soon as the leading edge of the sheet is under the catch hooks 4, the cam 26 rocks the lever 10 to the position shown in FIG. 3 whereby the catch hooks 4 of the front stops 3 are lowered and the front stop member 5 aligns the leading edge of the sheet. Simultaneously with the lowering of the front stops 3, the suction pipes 11 are lowered, and

I specifically, lowered to the extent that they essentially draw in only air below the feed table plate 1 and therefore produce no underpressure, or only slight underpressure, above the feed table plate 1, so that the alignment movements of the sheet are not impeded or impaired by portions of the sheet sticking through suction at the feed table plate 1 or at the top side of the suction discs 23.

As soon as the sheet 2 is aligned, the front stops 3 are swung away by means of the shaft 6 so that the auxili- I arygripper 29, which has already gripped the leading edge of the sheet, can pass the sheet 2 to the gripper set 7 on the printing cylinder 8. While the departing sheet 9 is still being placed around the printing cylinder 8, the alignment of a new incoming sheet 2 has already started to take place.

It will be understood that the invention is not limited to the specific embodiments shown and that other alternate embodiments may be used. For example, a separate control mechanism may be provided for the suction pipes. Also in cases where movable'catch hooks are arranged ahead of the front stops for guiding the incoming sheets, the suction tubes may be arranged aheadof the movable catch hooks instead of ahead of the front stops.

We claim:

opening means comprising holes in said table smaller than said suction end of said suction conduit means so that said suction end does not come in contact with said sheets, and actuating means for raising and lowering said suction conduit means so that said open suction end thereof travels between a lowermost and an uppermost position thereof located below said feed table in synchronism with the operating cycle of the apparatus, whereby the underpressure applied from said open end of said suction conduit means through said suction opening means to the sheet to hold the latter down on said feed table is varied in synchronism with the operation of the apparatus.

2. Apparatus according to claim 1 wherein said suction conduit means comprises a suction conduit having one longitudinal end thereof arranged in underlying alignment with said suction opening means in said feed table.

3. Apparatus according to claim 2 wherein a plurality of groups of suction opening means are provided in said feed table and each group has a suction conduit associated therewith, the axes of said suction conduits being disposed generally perpendicular to the top surface of said feed table.

4. Apparatus according to claim 1 wherein said actuating means comprises a pivotal lever for operating said stop means, said suction conduit means being mounted on said lever whereby said stop means are operable simultaneously with the raising and lowering of said suction conduit means.

5. Apparatus according to claim 4 further comprising cam means operating said pivotal lever in synchronism with the operating cycle of the sheet feeding apparatus.

6. Apparatus according to claim 1 wherein a plurality of suction opening means and suction conduit means are provided and means are provided for controlling the suction pressure in one or more of said suction conduit means.

7. Apparatus for feeding a succession of sheets comprising a feed table receiving said sheets, stop means at the front end of said feed table engaging the front edge of said sheets, suction opening means in said feed table preceding said stops, suction conduit means underlying said suction opening means in said feed table, and actuating means for raising and lowering said suction conduit means relative to said feed table in synchronism with the operating cycle of the apparatus, whereby the underpressure applied to the sheet to hold the latter down on said feed table is varied in synchronism with the operation of the apparatus, said suction opening 

1. Apparatus for feeding a succession of sheets comprising a feed table receiving said sheets, stop means at the front end of said feed table engaging the front edge of said sheets, suction opening means formed in said feed table preceding said stop means, suction conduit means having an open suction end located beneath said suction opening means in said feed table, said suction opening means comprising holes in said table smaller than said suction end of said suction conduit means so that said suction end does not come in contact with said sheets, and actuating means for raising and lowering said suction conduit means so that said open suction end thereof travels between a lowermost and an uppermost position thereof located below said feed table in synchronism with the operating cycle of the apparatus, whereby the underpressure applied from said open end of said suction conduit means through said suction opening means to the sheet to hold the latter down on said feed table is varied in synchronism with the operation of the apparatus.
 2. Apparatus according to claim 1 wherein said suction conduit means comprises a suction conduit having one longitudinal end thereof arranged in underlying alignment with said suction opening means in said feed table.
 3. Apparatus according to claim 2 wherein a plurality of groups of suction opening means are provided in said feed table and each group has a suction conduit associated therewith, the axes of said suction conduits being disposed generally perpendicular to the top surface of said feed table.
 4. Apparatus according to claim 1 wherein said actuating means comprises a pivotal lever for operating said stop means, said suction conduit means being mounted on said lever whereby said stop means are operable simultaneously with the raising and lowering of said suction conduit means.
 5. Apparatus according to claim 4 further comprising cam means Operating said pivotal lever in synchronism with the operating cycle of the sheet feeding apparatus.
 6. Apparatus according to claim 1 wherein a plurality of suction opening means and suction conduit means are provided and means are provided for controlling the suction pressure in one or more of said suction conduit means.
 7. Apparatus for feeding a succession of sheets comprising a feed table receiving said sheets, stop means at the front end of said feed table engaging the front edge of said sheets, suction opening means in said feed table preceding said stops, suction conduit means underlying said suction opening means in said feed table, and actuating means for raising and lowering said suction conduit means relative to said feed table in synchronism with the operating cycle of the apparatus, whereby the underpressure applied to the sheet to hold the latter down on said feed table is varied in synchronism with the operation of the apparatus, said suction opening means comprising a disc having a plurality of openings, said feed table having a recessed opening in which said disc is received, said disc being positioned such that the top surface thereof is flush with the top surface of said feed table. 